The present invention relates generally to a method for treating a polyimide surface, and, more particularly, to a method for treating a polyimide surface using amines.
Polyimide has a small coefficient of thermal expansion and a small dielectric constant, and exhibits good heat resistance and dimensional stability, and is widely used as a composite material, an adhesive, and a coating material. These polyimide characteristics of good heat resistance, low dielectric constant, and good mechanical properties make polyimide particularly useful as a dielectric or protective layer in semiconductor devices, e.g., in semiconductor memory devices such as DRAMs and SRAMs. In such applications, the polyimide preferably interfaces with metals, ceramics, and polymers such as epoxy molding compounds. Therefore, the adhesion of polyimide to these materials is an important factor with respect to the reliability of semiconductor devices.
Generally, polyimide is formed by synthesizing polyamic acid, a precursor of polyimide, by polymerizing dianhydride with diamine in a solvent. The polyamic acid is transformed into polyimide by means of a dehydration process, which is carried out by means of application of heat and/or by means of a dehydrant.
PMDA-ODA (pyromellitic dianhydride-4,4'-oxydianiline) polyimide exhibits poor adhesion to silicon wafers. Epoxy resin/PMDA-ODA or epoxy molding compound/PMDA-ODA exhibit such poor adhesion that spontaneous peeling occurs. Consequently, extensive research & development has been devoted to improving such poor adhesion. A first method which has been proposed is directed to changing the chemical structure of the main chain of the polyimide using a co-monomer such as BTDA (benzophenone tetracarboxyl dianhydride) or GAPDS (bis (.gamma.-aminopropyl) tetramethyldisiloxane), to thereby form a copolymerized polyimide. A second method which has been proposed is directed to plasma treatment of the polyimide. A third method which has been proposed is directed to wet surface treatment of the polyimide, in which the imide functional group of the polyimide is hydrolzyed into amic acid by treating the polyimide with aqueous sodium hyrodxide (or aqueous potassium hydroxide) solution and then with an aqueous hydrochloric acid solution.
Although the above-described proposed methods improve the adhesion of polyimide to silicon, epoxy resin, and other materials, they still suffer from the following drawbacks and shortcomings. Namely, copolymerized polyimide exhibits a decrease in heat resistance as compared with PMDA-ODA without a co-monomer. Wet surface treatment of polyimide in an alkali solution takes a relatively long time, and subjects metal lines of the semiconductor device to corrosion by hydroxide ions left on the polyimide surface.
Based on the above, it can be appreciated that there presently exists a need in the art for a method of treating a polyimide surface which overcomes the above-described drawbacks and shortcomings of the presently available methods of treating a polyimide surface. The present invention fulfills this need.